You're deluding yourself
Starting with--you're WAY overestimating the capacity of your holding tank. I don't know what size it is, but let's do the math: Each flush puts at LEAST a half gallon into it, so a 15 gallon tank is only good for a max of about 30 flushes...you'd be safer estimating 20. Figure at least 4 flushes/person/day, and that's only about two 2-person weekends aboard. A 20 gallon tank would give you at most another day. And you've only pumped out once, earlier this season? Your tank has been overflowing out the vent--which, btw, is NOT an overflow...NOTHING but air should ever pass through it, or it will clog up, and then you have REAL problems!--for weeks! So no...all is prob'ly not well...'cuz your tank vent is almost certainly clogged, or the waste wouldn't have backed up into the toilet or spray waste out "the raised cylinder" (which I THINK may be a filter...if it is, it's toast, 'cuz they can't get wet). That happened because flushing the head pressurized the tank. That means running the macerator didn't empty the tank, either...just a gallon or two till it pulled a vacuum. First, clear the vent. If that "raised cylinder" is in fact a filter, remove it and either replace it--which will cost you $50--or replace the entire vent hose (whether there's a filter in it or not, I'd replace the hose...it's a whole lot easier than trying to clean it out)...use white sanitation hose. Blast out the vent thru-hull with a hose till it's clear. Then go to a pumpout to empty the tank, followed by a THOROUGH rinsing out of your whole system with clean fresh water...pump bucketfuls down the head during pumpout, then once the tank is empty, stick a hose (NOT a hose used for filling water tanks!) down the pumpout and let it run till water runs out the vent and keeps running out till it's clear. Finally, replace the joker valve in your toilet. It's a rubber cup-shaped valve in the head discharge fitting. We'll deal with getting rid of the odor from the spill in your boat later. But from now on, unless you want to install a gauge (which I highly recommend doing), either dump your tank (which, btw, is illegal unless you're at least 3 miles out to sea) at the end of every weekend or have it pumped out every other weekend, and check your tank vent thru-hull regularly for blockage...blast it out with water every time you wash your boat. And please read the articles in the Head Mistress Reference Library to learn how to maintain your system and prevent problems in the future.
